Non-noble metal based catalyst and method of manufacturing the same

ABSTRACT

In an aspect of the present inventions, provided herein is a non-noble metal-based catalyst for an electrode of a fuel cell. The non-noble metal-based catalyst comprise a porous carbon having a first pore and a second pore smaller than the first pore. The first pore has a pore size of about 5 to 100 nm and has an inner wall into which an active site of the non-noble metal-based catalyst is introduced.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present application claims under 35 U.S.C. § 119(a) the benefit ofKorean Patent Application No. 10-2016-0175354, filed on Dec. 21, 2016,the entire contents of which is incorporated herein for all purposes bythis reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relate to non-noble metal-based catalysts used aselectrode materials for fuel cells, and methods of manufacturing thesame.

Description of Related Art

In conventional proton exchange membrane fuel cells (PEMFCs), fineparticles including a noble metal with high catalytic activity and highpotential, particularly, platinum, as a main ingredient, have beenwidely used as an electrode catalyst.

However, since platinum is a rare metal having a high cost, a need todevelop alternative non-noble metal-based catalysts for oxygen reductionreaction of fuel cells having high activity and replacing platinumcatalysts is increasing.

Research has been conducted into a method of using an additive such aszirconium oxide to reduce the use of platinum. A method of manufacturinga transition metal oxynitride electrode catalyst by attaching oxynitrideof a transition metal to the surface of a support material by sputteringhas been reported.

However, non-noble metal-based electrode catalysts currently availablehave unsatisfactory catalytic activity, and thus performance of fuelcells including the same can be improved.

The information disclosed in this Background of the Invention section isonly for enhancement of understanding of the general background of theinvention and should not be taken as an acknowledgement or any form ofsuggestion that this information forms the prior art already known to aperson skilled in the art.

BRIEF SUMMARY

Various aspects of the present invention are directed to providing anon-noble metal-based catalyst having a catalytic active siteselectively positioned on the surfaces of micropores and a method ofmanufacturing the same. According to an exemplary embodiment of thepresent invention, types of non-noble metal-based catalyst precursorsused to manufacture non-noble metal-based catalysts and processingparameters therefor may be controlled.

Additional aspects of the disclosure will be set forth in part in thedescription which follows and, in part, will be obvious from thedescription, or may be learned by practice of the disclosure.

In an aspect of the present inventions, there is provided a non-noblemetal-based catalyst for an electrode of a fuel cell. The non-noblemetal-based catalyst comprise a porous carbon having a first pore and asecond pore smaller than the first pore, the first pore has a pore sizeof about 5 to 100 nm (e.g., about 5 nm, 10, 15, 20, 25, 30, 35, 40, 45.50, 55, 60, 65, 70, 75, 80. 85. 90. 95 or about 100 nm) and has an innerwall into which an active site of the non-noble metal-based catalyst isintroduced.

The porous carbon may have a structure in which the first pore and thesecond pore are uniformly connected in a three-dimensional space.

The first pore may have a pore size of about 15 to 60 nm (e.g., about15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32,33, 34, 35, 36, 37, 38,39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50,51, 52, 53, 54, 55, 56, 57, 58, 59, or about 60 nm).

An active site of the non-noble metal-based catalyst may be provided ina form represented by Formula 1 below:M_(x)N_(y)  Formula 1

wherein x is an integer from 0 to 1, y is an integer from 1 to 4, and Mis a transition metal.

The active site of the non-noble metal-based catalyst may be formed by anon-noble metal-based catalyst precursor.

The non-noble metal-based catalyst precursor may have a form in which atleast one of phthalocyanine, phthalocyanine tetrasulfonate, octabutoxyphthalocyanine, hexadecafluoro phthalocyanine, octakis octyloxyphthalocyanine, tetra-tert-butyl phthalocyanine, tetraazaphthalocyanine, tetraphenoxy phthalocyanine, tetra-tert-butyl tetrakisdimethylamino phthalocyanine, tetrakis cumylphenoxy phthalocyanine,tetrakis pyridiniomethyl phthalocyanine, tetranitrophthalocyanine,naphthalocyanine, tetra-tert-butyl naphthalocyanine, tetraphenylporphine, tetrakis pentafluorophenyl porphyrin, tetrakis methylpyridinioporphyrin tetratoluenesulfonate, tetrakistrimethylammoniophenylporphyrin tetratoluenesulfonate, tetramethyl divinyl porphinedipropionicacid, tetrapyridyl porphine, octaethyl porphyrin, tetrakis methoxyphenylporphine, tetraphenylporphine tetracarboxylic acid, tetrakishydroxyphenyl porphine, tetrakis sulfonatophenyl porphine,etioporphyrin, 1,10-phenanthroline,1,10-phenanthroline-5,6-dionedimethyl-1,10-phenanthroline,dimethyl-1,10-phenanthroline, dimethoxy-1,10-phenanthroline,dimethoxy-1,10-phenanthroline, amino-1,10-phenanthroline,methyl-1,10-phenanthroline, dihydroxy-1,10-phenanthroline,tetramethyl-1,10-phenanthroline, chloro-1,10-phenanthroline,dichloro-1,10-phenanthroline, nitro-1,10-phenanthroline,bromo-1,10-phenanthroline, tetrabromo-1,10-phenanthroline,pyrazino[1,10]phenanthroline, diphenyl-1,10-phenanthroline, dimethyldiphenyl-1,10-phenanthroline, ethenyl formyl(hydroxytrimethyltetradecyl) trimethyl porphine dipropanoato, diethenyltetramethyl porphine dipropanoato, bis((amino carboxyethyl)thio)ethyltetramethyl porphine dipropanoato, dihydro dihydroxy tetramethyl divinylporphine dipropionic acid lactonato, ethenyl(hydroxy trimethyltetradecatrienyl) tetramethyl porphine dipropanoato, carboxyethenylcarboxyethyl dihydro bis(hydroxymethyl) tetramethyl porphinedicarboxylato, (dimethylbenzimidazolyl)cyanocobamide, curtis macrocycle,Jäger macrocycle and DOTA macrocycle, is coordinated to a metal.

The metal may comprise at least one transition metal selected from iron(Fe), cobalt (Co), manganese (Mn), nickel (Ni), and chromium (Cr).

The non-noble metal-based catalyst precursor may comprise a transitionmetal having a weight of about 1 to 50 wt % (e.g., about 1 wt %, 2, 3,4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22,23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,41, 42, 43, 44, 45, 46, 47, 48, 49, or about 50 wt %) based on a totalweight of the porous carbon.

The porous carbon may have an anchoring site introduced into a surfaceof a pore of the porous carbon to enhance interactions between theporous carbon and the non-noble metal-based catalyst precursor.

According to another aspect of the present invention, there is provideda method of manufacturing a non-noble metal-based catalyst for anelectrode of a fuel cell. The method may comprise mixing a porous carbonwith a non-noble metal-based catalyst precursor; heat-treating themixture at a temperature of about 600 to 1200° C. (e.g., about 600° C.,650° C., 700° C., 750° C., 800° C., 850° C., 900° C., 950° C., 1000° C.,1100° C., or about 1200° C.); stirring the heat-treated mixture in anacidic solution; and washing and drying the stirred mixture.

The porous carbon may have a first pore and a second pore smaller thanthe first pore, and the first pore has a pore size of 5 to 100 nm in themixing of the porous carbon with the non-noble metal-based catalystprecursor.

The first pore may have a pore size of 15 to 60 nm (e.g., about 15, 16,17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34,35, 36, 37, 38,39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52,53, 54, 55, 56, 57, 58, 59, or about 60 nm).

The method may further comprise heat-treating solid powder acquiredafter the drying in an ammonia (NH₃) gas atmosphere at a temperature ofabout 600° C. to about 1200° C. (e.g., about 600° C., 650° C., 700° C.,750° C., 800° C., 850° C., 900° C., 950° C., 1000° C., 1100° C., orabout 1200° C.) for about 5 to 60 minutes (e.g., about 5 minutes, 10,15, 20, 25, 30, 35, 40, 45, 50, 55, or about 60 minutes).

The method may further comprise forming an anchoring site on a surfaceof a pore of the porous carbon by heat-treating the porous carbon in anammonia (NH₃) gas atmosphere at a temperature of about 600° C. to about1200° C. (e.g., about 600° C., 650° C., 700° C., 750° C., 800° C., 850°C., 900° C., 950° C., 1000° C., 1100° C., or about 1200° C.) for about 5to 60 minutes (e.g., about 5 minutes, 10, 15, 20, 25, 30, 35, 40, 45,50, 55, or about 60 minutes).

The non-noble metal-based catalyst precursor may have a form in which atleast one of phthalocyanine, phthalocyanine tetrasulfonate, octabutoxyphthalocyanine, hexadecafluoro phthalocyanine, octakis octyloxyphthalocyanine, tetra-tert-butyl phthalocyanine, tetraazaphthalocyanine, tetraphenoxy phthalocyanine, tetra-tert-butyl tetrakisdimethylamino phthalocyanine, tetrakis cumylphenoxy phthalocyanine,tetrakis pyridiniomethyl phthalocyanine, tetranitrophthalocyanine,naphthalocyanine, tetra-tert-butyl naphthalocyanine, tetraphenylporphine, tetrakis pentafluorophenyl porphyrin, tetrakis methylpyridinioporphyrin tetratoluenesulfonate, tetrakistrimethylammoniophenylporphyrin tetratoluenesulfonate, tetramethyl divinyl porphinedipropionicacid, tetrapyridyl porphine, octaethyl porphyrin, tetrakis methoxyphenylporphine, tetraphenylporphine tetracarboxylic acid, tetrakishydroxyphenyl porphine, tetrakis sulfonatophenyl porphine,etioporphyrin, 1,10-phenanthroline,1,10-phenanthroline-5,6-dionedimethyl-1,10-phenanthroline,dimethyl-1,10-phenanthroline, dimethoxy-1,10-phenanthroline,dimethoxy-1,10-phenanthroline, amino-1,10-phenanthroline,methyl-1,10-phenanthroline, dihydroxy-1,10-phenanthroline,tetramethyl-1,10-phenanthroline, chloro-1,10-phenanthroline,dichloro-1,10-phenanthroline, nitro-1,10-phenanthroline,bromo-1,10-phenanthroline, tetrabromo-1,10-phenanthroline,pyrazino[1,10]phenanthroline, diphenyl-1,10-phenanthroline, dimethyldiphenyl-1,10-phenanthroline, ethenyl formyl(hydroxytrimethyltetradecyl) trimethyl porphine dipropanoato, diethenyltetramethyl porphine dipropanoato, bis((amino carboxyethyl)thio)ethyltetramethyl porphine dipropanoato, dihydro dihydroxy tetramethyl divinylporphine dipropionic acid lactonato, ethenyl(hydroxy trimethyltetradecatrienyl) tetramethyl porphine dipropanoato, carboxyethenylcarboxyethyl dihydro bis(hydroxymethyl) tetramethyl porphinedicarboxylato, (dimethylbenzimidazolyl)cyanocobamide, curtis macrocycle,Jäger macrocycle and DOTA macrocycle, is coordinated to a metal, in themixing of the porous carbon with the non-noble metal-based catalystprecursor.

The metal may comprise at least one transition metal selected from iron(Fe), cobalt (Co), manganese (Mn), nickel (Ni), and chromium (Cr).

The non-noble metal-based catalyst precursor may comprise a transitionmetal having a weight of 1 to 50 wt % based on a total weight of theporous carbon, in the mixing of the porous carbon with the non-noblemetal-based catalyst precursor.

The heat-treating of the mixture at a temperature of 600 to 1200° C. maycomprise heat-treating the mixture in an inert gas atmosphere at atemperature of 600 to 1200° C. for 10 to 300 minutes.

The stirring of the heat-treated mixture in an acidic solution maycomprise adding the heat-treated mixture to an acidic solution having aconcentration of 0.1 M or greater and stirring the resultant mixture.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of a non-noble metal-basedcatalyst for fuel cell electrodes according to an embodiment.

FIG. 2 is an exploded view of a portion A of FIG. 1.

FIG. 3 is a transmission electron microscopic (TEM) image of a structureof MSUFC porous carbon.

FIG. 4 is a graph illustrating pore size distribution of micropores ofthe MSUFC porous carbon.

FIG. 5 is a graph illustrating pore size distribution of ultrafine poresof the MSUFC porous carbon.

FIG. 6 is a TEM image of a structure of a final non-noble metal-basedcatalyst.

FIG. 7 is a graph illustrating pore size distribution of micropores ofthe non-noble metal-based catalyst.

FIG. 8 is a diagram schematically illustrating a reaction taking placeon the surface of a pore of the porous carbon into which an anchoringsite is not introduced.

FIG. 9 is a diagram schematically illustrating a reaction taking placeon the surface of a pore of the porous carbon into which an anchoringsite is introduced.

FIG. 10 is a schematic diagram illustrating a process of manufacturing anon-noble metal-based catalyst according to an embodiment.

FIG. 11 is a flowchart for describing the process of manufacturing thenon-noble metal-based catalyst.

FIG. 12 is a graph illustrating results of oxygen reduction reaction(ORR) with respect to the types of the non-noble metal-based catalystprecursor.

FIG. 13 is a graph illustrating results of illustrating oxygen reductionreaction (ORR) depending on introduction of anchoring sites.

FIG. 14 is a graph illustrating results of ORR with respect toheat-treatment conditions.

FIG. 15 and FIG. 16 are graphs illustrating Koutecky-Levich plots.

FIG. 17 is a graph illustrating changes in performance of single cellswith respect to spraying methods.

FIG. 18 is a graph illustrating changes in performance of single cellswith respect to mass ratio of the Nafion ionomer to the non-noblemetal-based catalyst, which are added to the catalyst solution.

FIG. 19 is a graph illustrating changes in performance of single cellswith respect to loading amounts of a catalyst.

FIG. 20 is a graph illustrating durability test results of single cells.

FIG. 21 is a diagram illustrating reaction of reactants in accordancewith positions of catalytic active sites.

FIG. 22 and FIG. 23 are graphs illustrating ORR results and changes inperformance of single cells with respect to positions of the catalyticactive sites.

It should be understood that the appended drawings are not necessarilyto scale, presenting a somewhat simplified representation of variousfeatures illustrative of the basic principles of the invention. Thespecific design features of the present invention as disclosed herein,including, for example, specific dimensions, orientations, locations,and shapes will be determined in part by the particular intendedapplication and use environment.

In the figures, reference numbers refer to the same or equivalent partsof the present invention throughout the several figures of the drawing.

DETAILED DESCRIPTION

Reference will now be made in detail to various embodiments of thepresent invention(s), examples of which are illustrated in theaccompanying drawings and described below. While the invention(s) willbe described in conjunction with exemplary embodiments, it will beunderstood that the present description is not intended to limit theinvention(s) to those exemplary embodiments. On the contrary, theinvention(s) is/are intended to cover not only the exemplaryembodiments, but also various alternatives, modifications, equivalentsand other embodiments, which may be included within the spirit and scopeof the invention as defined by the appended claims.

Also, it is to be understood that the terms “include” or “have” areintended to indicate the existence of elements disclosed in thespecification, and are not intended to preclude the possibility that oneor more other elements may exist or may be added.

In this specification, terms “first,” “second,” etc. are used todistinguish one component from other components and, therefore, thecomponents are not limited by the terms.

An expression used in the singular encompasses the expression of theplural, unless it has a clearly different meaning in the context.

The reference numerals used in operations are used for descriptiveconvenience and are not intended to describe the order of operations andthe operations may be performed in a different order unless otherwisestated.

The present invention relates to a nanoporous non-noble metal-basedcatalyst having a uniform structure, and a method of manufacturing thesame.

The non-noble metal-based catalyst according to an exemplary embodimentof the present invention is used in oxygen reduction reaction takingplace in cathodes of proton exchange membrane fuel cells (PEMFCs). Thenon-noble metal-based catalyst may be prepared by doping a non-noblemetal-based catalyst precursor into a carbon composite having macroporeson the surface thereof. Thus, manufacturing costs may be reduced incomparison with the conventional platinum catalyst, and the non-noblemetal-based catalyst having several tens of nanoscale pores may reducemass transfer resistance in a membrane electrode assembly (MEA).

Hereinafter, a structure of the non-noble metal-based catalyst for fuelcell electrodes according to an exemplary embodiment will be describedand then the method of manufacturing the same will be described.

FIG. 1 is a schematic cross-sectional view of a non-noble metal-basedcatalyst for fuel cell electrodes according to an embodiment. FIG. 2 isa magnified view of a portion A of FIG. 1.

Referring to FIGS. FIG. 1 and FIG. 2, the non-noble metal-based catalystfor fuel cell electrodes has a structure in which active sites of thenon-noble metal-based catalyst are introduced into inner walls of poresof porous carbon.

While a platinum catalyst used in general fuel cell electrodes is loadedon the surface of carbon, the non-noble metal-based catalyst accordingto an exemplary embodiment is formed by doping the non-noble metal-basedcatalyst precursor into the porous carbon structure, in other words, byintroducing a non-noble metal-based catalyst precursor into a carbonnetwork structure of the porous carbon.

As the porous carbon, a porous carbon material having pores may be used.The pores of the surface of the porous carbon may include first poresand second pores smaller than the first pores. More particularly, thefirst pores of the porous carbon may have a pore size of about 5 to 100nm (e.g., about 5 nm, 10, 15, 20, 25, 30, 35, 40, 45. 50, 55, 60, 65,70, 75, 80. 85. 90. 95 or about 100 nm), preferably, 15 to 50 nm (e.g.,about 5 nm, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21,22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38,39,40, 41, 42, 43, 44, 45, 46, 47, 48, 49, or about 50 nm). The secondpores may have a pore size of several nm that is the smallest pore sizeobtained during the preparation of the porous carbon. Throughout thespecification, the first pores may be referred to as micropores, and thesecond pores may be referred to as ultrafine pores.

The first pores and the second pores may form a uniformly connectedstructure in a three-dimensional space. Hereinafter, a structure of theporous carbon and pore size distribution data will be described based onMSUFC porous carbon used herein.

FIG. 3 is a transmission electron microscopic (TEM) image of a structureof MSUFC porous carbon. FIG. 4 is a graph illustrating pore sizedistribution of micropores of the MSUFC porous carbon. FIG. 5 is a graphillustrating pore size distribution of ultrafine pores of the MSUFCporous carbon.

Referring to FIGS. FIG. 3 and FIG. 4, it is confirmed that microporeshaving a pore size of about 15 to about 60 nm are formed on the surfaceof the MSUFC porous carbon and a channel having a size of about 2 toabout 10 nm is formed therein. Also, referring to FIGS. 3 and 5, it isconfirmed that ultrafine pores having a pore size of about 0.5 to about1.5 nm are formed on the surface of the MSUFC porous carbon.

In general, if the pore size of the porous carbon is less than 15 nm,mass transfer resistance may increase. If the pore size of the porouscarbon is greater than 60 nm, specific surface area of the porous carbonmay decrease. Thus, the first pores having a pore size of about 5 to 100nm (e.g., about 5 nm, 10, 15, 20, 25, 30, 35, 40, 45. 50, 55, 60, 65,70, 75, 80. 85. 90. 95, or about 100 nm), preferably, 5 to 60 nm (e.g.,about 5 nm, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21,22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38,39,40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57,58, 59, or about 60 nm), may be introduced into the carbon structureaccording to an exemplary embodiment to obtain satisfactory masstransfer resistance and specific surface area.

Active sites of the non-noble metal-based catalyst are formed on theinner walls of the first pores of the porous carbon as illustrated inFIG. 3. The active sites of the non-noble metal-based catalyst may beformed by using a non-noble metal-based catalyst precursor. According tothe present embodiment, a non-noble metal-based catalyst precursorhaving a diameter less than that of the first pores and greater thanthat of the second pores may be used to control conditions for themanufacturing process, such that the active sites of the non-noblemetal-based catalyst are selectively formed on the surfaces of the firstpores.

For example, if iron phthalocyanine having a diameter of about 1.2 nm isused as the non-noble metal-based catalyst precursor, most of the secondpores are smaller than the non-noble metal-based catalyst precursors,and thus, almost all of the non-noble metal-based catalyst precursorsmay interact with the surfaces of the first pores to form the catalyticactive sites selectively on the inner walls of the first pores.Meanwhile, since the channel of the porous carbon has a size of about 2to about 10 nm as described above, the catalytic active site may also beformed on portions of the inner walls of the channel.

FIG. 6 is a TEM image of a structure of a final non-noble metal-basedcatalyst. FIG. 7 is a graph illustrating pore size distribution ofmicropores of the non-noble metal-based catalyst. FIGS. FIG. 6 and FIG.7 illustrate results of experiments in case of using iron phthalocyanineas the non-noble metal-based catalyst precursor.

The results shown in FIGS. FIG. 6 and FIG. 7 are compared with thoseshown in FIGS. FIG. 3 and FIG. 4. In case of the non-noble metal-basedcatalyst according to an exemplary embodiment in which the porous carbonis doped with the non-noble metal-based catalyst precursor, it may beconfirmed that the distribution of pores decreases after doping theporous carbon with the non-noble metal-based catalyst precursor. Thus,it may be confirmed that the non-noble metal-based catalyst precursor isdoped into the surfaces of the channel structure and the first pores ofthe porous carbon and the active sites are formed.

The non-noble metal-based catalyst precursor may have a form in which atleast one of phthalocyanine, phthalocyanine tetrasulfonate, octabutoxyphthalocyanine, hexadecafluoro phthalocyanine, octakis octyloxyphthalocyanine, tetra-tert-butyl phthalocyanine, tetraazaphthalocyanine, tetraphenoxy phthalocyanine, tetra-tert-butyl tetrakisdimethylamino phthalocyanine, tetrakis cumylphenoxy phthalocyanine,tetrakis pyridiniomethyl phthalocyanine, tetranitrophthalocyanine,naphthalocyanine, tetra-tert-butyl naphthalocyanine, tetraphenylporphine, tetrakis pentafluorophenyl porphyrin, tetrakis methylpyridinioporphyrin tetratoluenesulfonate, tetrakistrimethylammoniophenylporphyrin tetratoluenesulfonate, tetramethyl divinyl porphinedipropionicacid, tetrapyridyl porphine, octaethyl porphyrin, tetrakis methoxyphenylporphine, tetraphenylporphine tetracarboxylic acid, tetrakishydroxyphenyl porphine, tetrakis sulfonatophenyl porphine,etioporphyrin, 1,10-phenanthroline,1,10-phenanthroline-5,6-dionedimethyl-1,10-phenanthroline,dimethyl-1,10-phenanthroline, dimethoxy-1,10-phenanthroline,dimethoxy-1,10-phenanthroline, amino-1,10-phenanthroline,methyl-1,10-phenanthroline, dihydroxy-1,10-phenanthroline,tetramethyl-1,10-phenanthroline, chloro-1,10-phenanthroline,dichloro-1,10-phenanthroline, nitro-1,10-phenanthroline,bromo-1,10-phenanthroline, tetrabromo-1,10-phenanthroline,pyrazino[1,10]phenanthroline, diphenyl-1,10-phenanthroline, dimethyldiphenyl-1,10-phenanthroline, ethenyl formyl(hydroxytrimethyltetradecyl) trimethyl porphine dipropanoato, diethenyltetramethyl porphine dipropanoato, bis((amino carboxyethyl)thio)ethyltetramethyl porphine dipropanoato, dihydro dihydroxy tetramethyl divinylporphine dipropionic acid lactonato, ethenyl(hydroxy trimethyltetradecatrienyl) tetramethyl porphine dipropanoato, carboxyethenylcarboxyethyl dihydro bis(hydroxymethyl) tetramethyl porphinedicarboxylato, (dimethylbenzimidazolyl)cyanocobamide, curtis macrocycle,Jäger macrocycle and DOTA macrocycle, is coordinated to a metal ion. Inthis case, the metal may include at least one transition metal selectedfrom the group consisting of iron (Fe), cobalt (Co), manganese (Mn),nickel (Ni), and chromium (Cr).

Meanwhile, the types of the non-noble metal-based catalyst precursor arenot limited thereto and may also be broadly understood as a conceptincluding modifications within a range obvious to those of ordinaryskill in the art.

The non-noble metal-based catalyst precursor may include a transitionmetal such that a weight of the transition metal is in the range ofabout 1 to 50 wt % (e.g., about 1 wt %, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11,12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29,30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47,48, 49, or about 50 wt %) based on a total weight of the porous carbon.

If the weight of the transition metal is less than 1 wt % based on thetotal weight of the porous carbon, the catalytic active sites may not beappropriately formed. If the weight of the transition metal is greaterthan 50 wt % based on the total weight of the porous carbon, all of thenon-noble metal-based catalyst precursors cannot enter the first poresof the porous carbon and are located on the surface of the porouscarbon. Thus, the weight of the transition metal needs to be adjustedbased on the total weight of the porous carbon.

Meanwhile, the porous carbon may have anchoring sites introduced intothe surfaces of pores of the porous carbon according to an exemplaryembodiment to increase interactions between the porous carbon and thenon-noble metal-based catalyst precursor. A process of introducing theanchoring sites into the surfaces of the pores of the porous carbon mayinclude doping the surface of the porous carbon with nitrogen atoms invarious manners before doping the surface of the porous carbon with thenon-noble metal-based catalyst precursor.

Hereinafter, probability of catalytic active site formation whenanchoring sites are introduced or not introduced into the pore surfacesof the porous carbon will be described with reference to theaccompanying drawings.

FIG. 8 is a diagram schematically illustrating a reaction taking placeon the surface of a pore of the porous carbon into which an anchoringsite is not introduced. FIG. 9 is a diagram schematically illustrating areaction taking place on the surface of a pore of the porous carbon intowhich an anchoring site is introduced.

Referring to FIG. 8, if the anchoring sites are not formed on the poresurfaces CS of the porous carbon, interactions between the carbonparticles on the pore surfaces CS and the non-noble metal-based catalystprecursors CP are weak, so that a probability of catalytic active siteformation decreases. In this case, transition metal particles MP may beformed on the pore surfaces CS of the porous carbon with the laps oftime. The transition metal particles MP may be eluted by an acidicsolution, which will be described later.

Referring to FIG. 9, if the anchoring sites AN are formed on the poresurfaces CS of the porous carbon, the anchoring sites AN may enhanceinteractions between carbon particles on the pore surfaces CS and thenon-noble metal-based catalyst precursors CP. In other words,agglomeration of the non-noble metal-based catalyst precursors CP may beprevented by enhancing interactions between carbon particles and thenon-noble metal-based catalyst precursors CP by using the nitrogen atomsdoped into the pore surfaces CS of the porous carbon as the anchoringsites AN. In addition, formation of the catalytic active sites A may beenhanced to increase the catalytic activity of the non-noble metal-basedcatalyst.

The active site A of the non-noble metal-based catalyst formed by thenon-noble metal-based catalyst precursor and the anchoring site may berepresented by Formula 1 below.M_(x)N_(y)  Formula 1

In Formula 1, x is an integer from 0 to 1, y is an integer from 1 to 4,and M is a transition metal such as iron (Fe), cobalt (Co), manganese(Mn), nickel (Ni), and chromium (Cr).

The structure of the non-noble metal-based catalyst for fuel cellelectrodes according to an exemplary embodiment has been describedabove. Hereinafter, a method of manufacturing the non-noble metal-basedcatalyst will be described.

FIG. 10 is a schematic diagram illustrating a process of manufacturing anon-noble metal-based catalyst according to an embodiment. FIG. 11 is aflowchart for describing the process of manufacturing the non-noblemetal-based catalyst.

Referring to FIGS. FIG. 10, and FIG. 11, the process of manufacturingthe non-noble metal-based catalyst according to an exemplary embodimentincludes mixing a porous carbon with a non-noble metal-based catalystprecursor (110), heat-treating the mixture (120), stirring theheat-treated mixture in an acidic solution (130), and washing and dryingthe stirred mixture (140).

First, the mixing of the porous carbon with the non-noble metal-basedcatalyst precursor includes preparing the porous carbon and mixing theporous carbon with the non-noble metal-based catalyst precursor.

The preparation of the porous carbon may include a process ofsynthesizing MSUFC. The process of synthesizing MSUFC is as follows.

First, 9 mL of furfuryl alcohol is mixed with 6 g of AIMSUF-Si whileadding the furfuryl alcohol by small quantities at a time, and themixture is maintained at room temperature in a vacuum for 30 minutes.Then, the vacuum state is maintained in an oven at 85° C. for 8 hours.Then, solid powder obtained therefrom is carbonized in an inert gasatmosphere at 850° C. for 2 hours. The carbonization is performed byincreasing the temperature to 600° C. at a rate of 1° C./min and to 850°C. at a rate of 5° C./min. Then, the carbonized solid powder is added toa 2 M sodium hydroxide (NaOH) solution and the mixture is stirred whilebeing heated in boiling water at 80° C. for 6 hours. Then, the resultantmixture is washed using distilled water under a reduced pressure untilthe resultant has a neutral pH and dried to obtain MSUFC.

However, the aforementioned method is an example of synthetizing MSUFC,and any other methods obvious to one of ordinary skill in the art mayalso be used therefor.

Upon completion of the synthesis of MSUFC, the porous carbon and thenon-noble metal-based catalyst precursor are mixed.

Types of the non-noble metal-based catalyst available during the mixingprocess of the porous carbon and the non-noble metal-based catalystprecursor are as described above. In this regard, the activity of oxygenreduction reaction is determined depending on the types of the non-noblemetal-based catalyst precursor. Hereinafter, results of experiments ofthe activity of oxygen reduction reaction depending on the experimentsof the non-noble metal-based catalyst precursor will be described forbetter understandings.

FIG. 12 is a graph illustrating results of oxygen reduction reaction(ORR) with respect to the types of the non-noble metal-based catalystprecursor.

FIG. 12 illustrates ORR results of first to fifth samples measured usinga 0.5 M oxygen-saturated sulfuric acid (H₂SO₄) solution, a non-noblemetal-based catalyst in a loading amount of 815 μg/cm², and 40 wt % Pt/Cin a loading amount of 16 μgpt/cm² at 1600 rpm.

In this regard, the first sample is a non-noble metal-based catalystsample using iron phthalocyanine as the non-noble metal-based catalystprecursor, the second sample is a non-noble metal-based catalyst sampleusing iron phenanthroline as the non-noble metal-based catalystprecursor, the third sample is a non-noble metal-based catalyst sampleusing vitamin B12 as the non-noble metal-based catalyst precursor, thefourth sample is a non-noble metal-based catalyst sample using 5, 10,15, 20-tetrakis(4-methoxyphenyl)-21H, 23H-porphine iron (III) chlorideas the non-noble metal-based catalyst precursor, and the fifth sample isa supported catalyst in which platinum (Pt) is supported on carbon.

As a result of analyzing half wave potentials measured at −3 mA/cm²based on the graph of FIG. 12, it may be confirmed that the fifth samplehas the highest half wave potential, and the half wave potentialdecreases in the order of the fourth sample, the first sample, the thirdsample, and the second sample. As the half wave potential increases, thecatalytic activity increases. Therefore, it may be confirmed that thefifth sample using the platinum catalyst has the highest catalyticactivity.

Meanwhile, it may also be confirmed that the half wave potentials of thefirst to fourth samples using the non-noble metal-based catalystprecursors are slightly lower than the half wave potential of the fifthsample. Thus, it may be confirmed that non-noble metal-based catalystshaving relatively excellent catalytic activity may be obtained using thenon-noble metal-based catalyst precursors with reduced manufacturingcosts therefor.

Meanwhile, the amount of the non-noble metal-based catalyst precursormay be adjusted such that the amount of the transition metal containedin the non-noble metal-based catalyst precursor is in the range of about1 to 50 wt % (e.g., about 1 wt %, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12,13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30,31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48,49, or about 50 wt %) based on the total weight of the porous carbon inthe mixing of the porous carbon with the non-noble metal-based catalystprecursor. The significance of the weight range of the transition metaladded to the porous carbon is as described above, and descriptionspresented above will not be repeated herein.

The mixing of the porous carbon with the non-noble metal-based catalystprecursor according to an exemplary embodiment may include introducinganchoring sites to the porous carbon. This process may be performed toenhance interactions between the porous carbon and the non-noblemetal-based catalyst precursor. However, this process may be dispensedwith.

FIG. 13 is a graph illustrating results of illustrating oxygen reductionreaction (ORR) depending on introduction of anchoring sites.

FIG. 13 illustrates ORR results of sixth to ninth samples measured usinga 0.5 M oxygen-saturated H₂SO₄ solution, a non-noble metal-basedcatalyst in a loading amount of 815 μg/cm², and 40 wt % Pt/C in aloading amount of 16 μg pt/cm² at 1600 rpm.

In this regard, the sixth sample is a non-noble metal-based catalystsample using 5, 10, 15, 20-tetrakis(4-methoxyphenyl)-21H, 23H-porphineiron(III) chloride as the non-noble metal-based catalyst precursor, theseventh sample is a non-noble metal-based catalyst sample using ironphthalocyanine as the non-noble metal-based catalyst precursor afterintroducing anchoring sites into the porous carbon, the eighth sample isa non-noble metal-based catalyst sample using 5, 10, 15,20-tetrakis(4-methoxyphenyl)-21H, 23H-porphine iron(III) chloride as thenon-noble metal-based catalyst precursor after introducing anchoringsites into the porous carbon, and the ninth sample is a supportedcatalyst in which platinum (Pt) is supported on carbon.

As a result of analyzing half wave potentials measured at −3 mA/cm²based on the graph of FIG. 13, it may be confirmed that the seventhsample has the highest half wave potential, and the half wave potentialdecreases in the order of the eighth sample, the ninth sample, and thesixth sample. Particularly, upon comparison between the sixth sample andthe eighth sample, it may be confirmed that the eighth sample havinganchoring sites introduced into the porous carbon using nitrogen has farhigher catalytic activity than the sixth sample with no anchoring sites.Also, since the catalytic activity of the seventh and eighth samples ishigher than that of the ninth sample using the noble metal catalyst, itmay be confirmed that a decrease in the catalytic activity caused byusing the non-noble metal-based catalyst may be prevented by introducingthe anchoring sites.

After the porous carbon is mixed with the non-noble metal-based catalystprecursor, the mixture may be heat-treated.

The heat-treatment of the mixture may be performed by heat-treating themixture at a temperature of 600 to 1200° C. in an inert gas atmospherefor about 10 to 300 minutes. Here, types of the inert gas may includeargon (Ar), nitrogen (N₂), helium (He), and neon (Ne), without beinglimited thereto.

If a heat-treatment temperature is lower than 600° C., the catalyticactive sites are not efficiently formed on the surface of the porouscarbon. If the heat-treatment temperature is higher than 1200° C., thestructure of the porous carbon may easily break. Meanwhile, sinceperformance of the ORR varies according to the heat-treatmenttemperature in the range of 600° C. to 1200° C., the heat-treatmentconditions may be adjusted appropriately depending on desired activityof the non-noble metal-based catalyst. Variation of the catalyticactivity depending on the heat-treatment conditions will be describedlater.

After heat-treating the mixture, the heat-treated mixture is added to anacidic solution and the resultant mixture may be stirred. This processis performed to remove inactive transition metal compounds.

The stirring of the heat-treated mixture in an acidic solution mayinclude adding the heat-treated mixture to an inorganic acidic solutionhaving a concentration of 0.1 M or greater and stirring the resultantmixture. Types of the inorganic acidic solution may include a 0.5 MH₂SO₄ solution, without being limited thereto.

Meanwhile, the acidic solution may have a concentration of 0.1 M orgreater. If the concentration of the acidic solution is less than 0.1 M,it may be difficult to sufficiently remove the inactive transition metalcompounds. Thus, the concentration of the acidic solution may beappropriately controlled, if required.

After this stirring process, the stirred mixture may be washed anddried. This process may include continuously washing the mixture usingdistilled water under a reduced pressure until the resultant has aneutral pH and then drying the washed mixture.

Meanwhile, after washing the stirred mixture and drying the washedmixture, solid powder obtained by the washing and drying process mayfurther be heat-treated in an ammonia (NH₃) gas atmosphere. In general,a carbon network of the porous carbon has defects. As nitrogen isintroduced into the defects of the porous carbon, the catalytic activitymay further be enhanced.

This process may include heat-treating the solid powder at a temperatureof about 600 to 1200° C. in an ammonia gas atmosphere for about 5 to 60minutes.

If the heat-treatment temperature is less than 600° C., the surface ofthe non-noble metal-based catalyst may not be efficiently doped withnitrogen. If the heat-temperature is greater than 1200° C., thestructure of the porous carbon may easily break. Also, if aheat-treatment time is less than 5 minutes, the surface of the non-noblemetal-based catalyst is not sufficiently doped with nitrogen. If theheat-treatment time is greater than 60 minutes, the structure of thenon-noble metal-based catalyst may easily break. Thus, theheat-treatment temperature and the heat-treatment time need to beappropriately adjusted to efficiently introduce nitrogen into thesurface of the porous carbon.

Hereinafter, variation of the catalytic activity in accordance with theheat-treatment conditions will be described with reference to theaccompanying drawings. Heat-treatment conditions in operations 120 and140 will be described in more detail based on the following experiments.

FIG. 14 is a graph illustrating results of ORR with respect toheat-treatment conditions.

FIG. 14 illustrates ORR results of tenth to thirteenth samples measuredusing a 0.5 M oxygen-saturated H₂SO₄ solution and a non-noblemetal-based catalyst in a loading amount of 815 μg/cm² at 1600 rpm.

In this regard, the tenth to thirteenth samples are non-noblemetal-based catalyst samples using iron phthalocyanine and heat-treatedunder different heat-treatment conditions. Particularly, the tenthsample is a non-noble metal-based catalyst sample heat-treated at 900°C. in an argon gas atmosphere for 60 minutes. The eleventh sample is anon-noble metal-based catalyst sample teat-treated at 900° C. in anargon gas atmosphere for 60 minutes, and then further heat-treated at950° C. in an ammonia gas atmosphere for 15 minutes. The twelfth sampleis a non-noble metal-based catalyst sample heat-treated at 1050° C. inan argon gas atmosphere for 60 minutes. The thirteenth sample is anon-noble metal-based catalyst sample heat-treated at 1050° C. in anargon gas atmosphere for 60 minutes, and then further heat-treated at950° C. in an ammonia gas atmosphere for 15 minutes.

As a result of analyzing half wave potentials measured at −3 mA/cm²based on the graph of FIG. 14, it may be confirmed that the tenth sampleheat-treated at 900° C. has better catalytic activity than the twelfthsample heat-treated at 1050° C. Meanwhile, it may also be confirmed thatthe catalytic activity is further enhanced via the additionalheat-treatment of the non-noble metal-based catalyst in the ammonia gasatmosphere based on comparison of the half wave potentials between thetenth and eleventh samples and between the twelfth and thirteenthsamples.

The method of manufacturing the non-noble metal-based catalyst accordingto an exemplary embodiment has been described above. Hereinafter,conditions for efficiently introducing the non-noble metal-basedcatalyst prepared as described above into an electrode structure of fuelcells will be described.

Meanwhile, there is a need to determine whether the non-noblemetal-based catalyst according to an exemplary embodiment has a 4-e pathbefore describing the conditions. If the non-noble metal-based catalysthas a 4-e path, water (H₂O) is generated by side reactions. However, ifthe non-noble metal-based catalyst has a 2-e path, hydrogen peroxide(H₂O₂) is generated by side reactions, thereby decreasing efficiency ofthe catalyst. Thus, hereinafter, analysis results of half cells will bedescribed in order to determine whether the non-noble metal-basedcatalyst has the 4-e path.

Analysis of half cells is designed as follows.

First, 10 mg of the synthesized non-noble metal-based catalyst isdispersed in a mixed solution of 2 ml ethanol and 10 μl of a 5 wt %Nafion solution for 30 minutes by sonication. Here, a non-noblemetal-based catalyst sample prepared by doping the porous carbon havinganchoring sites with the iron phthalocyanine catalyst precursor is usedas the non-noble metal-based catalyst sample to calculate the number ofelectron involved in reaction. Hereinafter, the non-noble metal-basedcatalyst sample prepared by doping the porous carbon having theanchoring sites with the iron phthalocyanine catalyst precursor may bereferred to as an N-Phth for descriptive convenience.

16 μl of the as-prepared solution is coated on a polished glassy carbonhaving diameter of 5 mm and dried at room temperature, and theaforementioned drying process is repeated once.

The electrode is connected to a rotating disk electrode and dipped inthe 0.5 M oxygen-saturated H₂SO₄ solution to measure ORR. Cyclicvoltammetry (CV) is performed until a voltage of a reversible hydrogenelectrode (RHE) reaches to 1.0 V from 0.05 V by 20 cycles by Linearsweep voltammetry (LSV) at a scan rate of 10 mV/s from 1.0 to 0.1 V. Inthis experiment, Koutecky-Levich plots illustrated in FIGS. 15 and 16are deduced while adjusting the electrode rotation speed from 400 rpm to2500 rpm, and the result values of the Koutecky-Levich plots are used tocalculate the number of electrons involved in the reaction.

The number of electrons involved in the reaction may be calculated usingthe following equations.

$\begin{matrix}{\frac{1}{\bullet} = {\frac{1}{\bullet_{\bullet}} + \frac{1}{\bullet_{\bullet}}}} & {{Equation}\mspace{14mu} 1} \\{j_{L} = {B\;\omega^{\frac{1}{2}}}} & {{Equation}\mspace{14mu} 2} \\{B = {0.62\; n\; F\;{CoDo}^{\frac{2}{3}}v^{\frac{- 1}{6}}}} & {{Equation}\mspace{14mu} 3}\end{matrix}$

In Equations 1 to 3, j_(k) is kinetic current, J_(L) is limitingcurrent, w is rotation speed, F is faraday constant, C₀ is O₂concentration, D_(O) is O₂ diffusion coefficient, and v is viscosity.

The number of electrons of the non-noble metal-based catalyst sampleaccording to an exemplary embodiment involved in the reaction calculatedby Equations 1 to 3 and the Koutecky-Levich plots is 3.95 at 0.7 V.

Based on the results of experiments, it may be confirmed that thenon-noble metal-based catalyst according to an exemplary embodiment hasa 4-e path. In other words, the non-noble metal-based catalyst accordingto an exemplary embodiment has high catalytic activity by eliminatingunnecessary side reactions.

Hereinafter, conditions for efficiently introducing the non-noblemetal-based catalyst into an electrode structure of fuel cells, in otherwords, experimental examples to deduce conditions to realize fuel cellsoptimized to the non-noble metal-based catalyst according to anexemplary embodiment will be described.

To this end, a single cell is assembled after manufacturing a membraneelectrode assembly and performance of the single cell is analyzed.

A process of manufacturing the membrane electrode assembly and a processof assembling the single cell are as follows.

First, a non-noble metal-based catalyst solution according to anexemplary embodiment is prepared. More particularly, 50 g of thenon-noble metal-based catalyst prepared by doping the porous carbonhaving anchoring sites with iron phthalocyanine is dispersed in 5 ml ofa mixed solution of a 5 wt % Nafion solution and isopropanol for 30minutes to prepare a non-noble metal-based catalyst solution.

Also, a platinum catalyst solution, as a material used to form an anodeof the membrane electrode assembly, is prepared as follows. 50 mg of aplatinum catalyst is dispersed in a mixed solution of 0.2 ml ofdistilled water, 5 ml of isopropanol, and 428.6 mg of a 5 wt % Nafionsolution for 30 minutes to prepare a platinum catalyst solution.

The non-noble metal-based catalyst solution is coated on the surface ofan electrode having an area of 1.5 cm×1.5 cm by hand spraying viacatalyst coated substrate (CCS) and catalyst coated membrane (CCM)methods. Then, a single cell is assembled by fastening at a torque of 25kgf*cm.

More particularly, the non-noble metal-based catalyst solution is coatedon carbon paper (SGL 35 BC) by the CCS method, and the non-noblemetal-based catalyst solution is coated on nafion membrane (Nafion 211)by the CCM method. Meanwhile, even when the coating is performed by theCCS method, a hot pressing is performed at 125° C. for 1 minute under apressure of 70 kgf/cm². In the same manner, the platinum catalystsolution is coated on carbon paper and Nafion membrane. Through thisprocess, 0.2 mg_(pt)/cm² of a platinum catalyst is loaded on an anode,and 0.5 to 3 mg/cm² of the non-noble metal-based catalyst is loaded on acathode.

Next, performance of the single cell is analyzed under the followingconditions.

Conditions for analyzing performance of the single cells commonlyapplied to FIGS. 17 to 20 are as follows. First, performance of thesingle cell is measured after maintaining the single cell with anopen-circuit voltage for 2 hours at 65° C. at 100 percent humidity whilesupplying hydrogen and air such that amounts of hydrogen and air are 1.5times and twice as much as those of stoichiometric amounts thereof,respectively. Methods of controlling conditions for the process will bedescribed in more detail later.

First, an optimal spraying method used to prepare the single cell willbe described with reference to FIG. 17.

FIG. 17 is a graph illustrating changes in performance of single cellswith respect to spraying methods. FIG. 17 illustrates comparison ofperformance between a single cell using an MEA prepared by the CCSmethod and a single cell using an MEA prepared by the CCM method. Here,0.2 mg_(pt)/cm² of a platinum catalyst is loaded on an anode, and 0.5mg/cm² of the N-Phth is loaded on a cathode. Meanwhile, a mass ratio ofNafion to the catalyst is 1:1.5 in the solution used while spraying.

Referring to FIG. 17, it may be confirmed that current density and powerdensity obtained by the CCM method are higher than those obtained by theCCS method at the same potential.

In general, a higher current density at the same potential indicateshigher catalytic activity, and a higher power density at the samepotential indicates better cell performance. Thus, it may be confirmedthat the single cell obtained by the CCM method has better performancethan that obtained by the CCS method.

Next, an optimal composition ratio of the catalyst solution used in themanufacture of the single will be described with reference to FIG. 18.

FIG. 18 is a graph illustrating changes in performance of single cellswith respect to mass ratio of the Nafion ionomer to the non-noblemetal-based catalyst, which are added to the catalyst solution. Here,0.2 mg_(pt)/cm² of a platinum catalyst is loaded on an anode, and 0.5mg/cm² of the N-Phth is loaded on a cathode. Meanwhile, the CCM methodis used as the spraying method.

All of fourteen to eighteenth samples used in this experiment are theN-Phth catalyst sample. In the preparation of the single cell using thenon-noble metal-based catalyst according to an embodiment, the catalystsolution is prepared by mixing the non-noble metal-based catalyst withthe Nafion ionomer and ethanol. To find out an optimal ratio of thenon-noble metal-based catalyst, different mass ratios of the Nafionionomer to the N-Phth catalyst are used in the fourteen to eighteenthsamples. Hereinafter, a mass ratio of the Nafion ionomer to the nonioniccatalyst in the preparation of the catalyst solution will be referred toas a Nafion to catalyst ratio (NCR) for descriptive convenience. Thefourteenth sample is prepared by adjusting the NCR to 1.5, the fifteenthsample is prepared by adjusting the NCR to 2, the sixteenth sample isprepared by adjusting the NCR to 2.5, the seventeenth sample is preparedby adjusting the NCR to 3, and the eighteenth sample is prepared byadjusting the NCR to 3.5.

The graph is interpreted in the same manner as FIG. 17. It may beconfirmed that the single cell exhibits the best performance at the NCRof 2.5. It may be confirmed that a relatively large amount of the Nafionionomer is required to efficiently use the non-noble metal-basedcatalyst according to an exemplary embodiment due to a wide surface areaof the catalyst. On the contrary, if the NCR is greater than 2.5,performance of the single cell deteriorates. Thus, it may be confirmedthat an excess of the Nafion ionomer may interrupt supply of oxygen,thereby deteriorating performance of the single cell.

Next, an optimal catalyst loading amount required to prepare a singlecell will be described with reference to FIG. 19.

FIG. 19 is a graph illustrating changes in performance of single cellswith respect to loading amounts of a catalyst. Here, 0.2 mg_(pt)/cm² ofa platinum catalyst is loaded on an anode, and a catalyst solutionhaving an NCR of 2.5 is loaded on the cathode by the CCM method.

All of nineteenth to twenty-second samples used in this experiment arethe N-Phth catalyst sample. To find out an optimal amount of thenon-noble metal-based catalyst, the amounts of the catalyst loaded onthe cathode in the preparation of the single cells are modified. Thenineteenth sample is obtained by adjusting the catalyst loading amountto 0.5 mg/cm². The twentieth sample is obtained by adjusting thecatalyst loading amount to 1.0 mg/cm². The twenty-first sample isobtained by adjusting the catalyst loading amount to 1.5 mg/cm². Thetwenty-second sample is obtained by adjusting the catalyst loadingamount of 3.0.

The graph is interpreted in the same manner as FIG. 17. It may beconfirmed that performance of the single cell is enhanced while thecatalyst loading amount increases from 0.5 mg/cm² to 3.0 mg/cm². This isbecause mass transfer resistance is efficiently reduced by pores havinga diameter of 20 nm or greater formed on the surface of the non-noblemetal-based catalyst according to an embodiment.

Next, durability test results of single cells manufactured by using thenon-noble metal-based catalyst according to an exemplary embodiment willbe described with reference to FIG. 20.

FIG. 20 is a graph illustrating durability test results of single cells.Here, 0.2 mg_(pt)/cm² of a platinum catalyst is loaded on an anode, and3.0 mg/cm² of the N-Phth catalyst is loaded on the cathode. In thisregard, the non-noble metal-based catalyst solution having an NCR of 2.5is loaded on the cathode by the CCM method.

First, initial performance of the single cell is measured, and theresult is shown as G1. Then, after 1500 cycles at 50 mV/s between 0.6 Vand 1.0 V, performance of the single cell is measured, and the result isshown as G2.

It may be confirmed that the activity is reduced by about 2.2% at 0.6 Vbased on the measured current densities. Thus, it may be confirmed thatthe single cell prepared using the non-noble metal-based catalystaccording to an exemplary embodiment has excellent durability.

Experimental examples to deduce conditions for implementing fuel cellsoptimized to the non-noble metal-based catalyst material according to anexemplary embodiment have been described.

According to the non-noble metal-based catalyst and the fuel cellmanufacturing using the same prepared according to the aforementionedmethods, catalytic active sites are only formed on the surface of largerpores among the pores of the porous carbon by adjusting conditions forthe manufacturing process. Thus, reactants easily approach the catalyticactive sites in an actual driving environment and the catalytic activesites may be more efficiently utilized.

Hereinafter, effects of the position of the catalytic active sites onenhancing utilization of the catalytic active sites will be describedwith reference to FIGS. 21 to 23.

FIG. 21 is a diagram illustrating reaction of reactants in accordancewith positions of catalytic active sites. FIGS. 22 and 23 are graphsillustrating ORR results and changes in performance of single cells withrespect to positions of the catalytic active sites.

If the a catalytic active site A is formed at the second pore H2 that isan ultrafine pore as illustrated in a left diagram of FIG. 21, areactant cannot easily approach the catalytic active site A, and thusfunctions of the catalytic active site A may not be efficientlyperformed.

On the contrary, in the non-noble metal-based catalyst sample accordingto an embodiment, the catalytic active site A is formed at the firstpore H1 that is a micropore as illustrated in a right diagram of FIG.21. Thus, functions of the catalytic active site A may be efficientlyperformed.

FIG. 22 illustrates ORR results of twenty-third to twenty-fifth samplesmeasured using a 0.5 M oxygen-saturated H₂SO₄ solution, a non-noblemetal-based catalyst in a loading amount of 815 μg/cm², and 40 wt % Pt/Cin a loading amount of 16 μgpt/cm² at 1600 rpm. The catalytic activesites are formed not only in the first pores but also the second poresin the twenty-third sample. The twenty-fourth sample is prepared byusing the N-Phth, and the twenty-fifth sample is prepared by using aplatinum catalyst commonly used in the art.

FIG. 23 illustrates changes in performance of the single cells preparedusing the twenty-third and twenty-fourth samples after maintaining thesingle cells at 65° C. while supplying hydrogen and air such thatamounts of hydrogen and air are 1.5 times and twice as much as those ofstoichiometric amounts thereof, respectively. Here, 0.2 mg_(pt)/cm² of aplatinum catalyst is loaded on an anode, 3.0 mg/cm² of the N-Phth isloaded on a cathode, and the NCR is 2.5 in the catalyst solution usedduring spraying.

Referring to FIGS. 22 and 23, it may be confirmed that voltage rapidlydecreases as the current density increases in the twenty-third sample inwhich the catalytic active sites are formed in the ultrafine pores. Thisis because mass transfer resistance increases due to difficulty inapproaching the catalytic active site.

However, the voltage does not rapidly decrease as the current densityincreases in the twenty-fourth sample and the twenty-fourth sampleexhibits better performance of the single cell than thetwenty-thirteenth sample.

Based on the results of experiments, it may be confirmed that thecatalytic active sites may be more efficiently used by allowing thereactants to easily approach the active sites in the actual drivingenvironment by selectively controlling the position of the catalyticactive sites formed at the pores of the porous carbon.

As is apparent from the above description, according to the non-noblemetal-based catalyst and the manufacturing method thereof, utilizationof the catalytic active sites may be enhanced by allowing the reactantsto easily approach the active sites in the actual driving environment byforming the active sites only on the surfaces of the micropores amongthe pores of the porous carbon by controlling conditions for themanufacturing process.

Also, excellent catalyst performance may be obtained by reducing masstransfer resistance in the membrane electrode assembly by introducing ananoporous carbon structure having a regular structure and relativelylarge pores thereinto.

Also, the catalytic activity may be improved by enhancing interactionswith the catalyst precursors by introducing anchoring sites into thesurface of the porous carbon.

The foregoing descriptions of specific exemplary embodiments of thepresent invention have been presented for purposes of illustration anddescription. They are not intended to be exhaustive or to limit theinvention to the precise forms disclosed, and obviously manymodifications and variations are possible in light of the aboveteachings. The exemplary embodiments were chosen and described in orderto explain certain principles of the invention and their practicalapplication, to thereby enable others skilled in the art to make andutilize various exemplary embodiments of the present invention, as wellas various alternatives and modifications thereof. It is intended thatthe scope of the invention be defined by the Claims appended hereto andtheir equivalents.

What is claimed is:
 1. A non-noble metal-based catalyst for an electrodeof a fuel cell comprising: a porous carbon having a first pore and asecond pore smaller than the first pore, wherein the first pore has apore size of about 5 to 100 nm and has an inner wall into which anactive site of the non-noble metal-based catalyst is introduced, whereinthe active site of the non-noble metal-based catalyst is formed by anon-noble metal-based catalyst precursor, and the non-noble metal-basedcatalyst precursor has a diameter less than that of the first pores andgreater than that of the second pores.
 2. The non-noble metal-basedcatalyst according to claim 1, wherein the porous carbon has a structurein which the first pore and the second pore are uniformly connected in athree-dimensional space.
 3. The non-noble metal-based catalyst accordingto claim 1, wherein the first pore has a pore size of about 15 to 60 nm.4. The non-noble metal-based catalyst according to claim 1, wherein anactive site of the non-noble metal-based catalyst is provided in a formrepresented by Formula 1 below:M_(x)N_(y)  Formula 1 wherein x is an integer from greater than 0 to 1,y is an integer from 1 to 4, and M is a transition metal selected fromiron (Fe), cobalt (Co), manganese (Mn), nickel (Ni) and chromium (Cr).5. The non-noble metal-based catalyst according to claim 1, wherein thenon-noble metal-based catalyst precursor has a form in which at leastone of phthalocyanine, phthalocyanine tetrasulfonate, octabutoxyphthalocyanine, hexadecafluoro phthalocyanine, octakis octyloxyphthalocyanine, tetra-tert-butyl phthalocyanine, tetraazaphthalocyanine, tetraphenoxy phthalocyanine, tetra-tert-butyl tetrakisdimethylamino phthalocyanine, tetrakis cumylphenoxy phthalocyanine,tetrakis pyridiniomethyl phthalocyanine, tetranitrophthalocyanine,naphthalocyanine, tetra-tert-butyl naphthalocyanine, tetraphenylporphine, tetrakis pentafluorophenyl porphyrin, tetrakis methylpyridinioporphyrin tetratoluenesulfonate, tetraki strimethylammoniophenylporphyrin tetratoluenesulfonate, tetramethyl divinyl porphinedipropionicacid, tetrapyridyl porphine, octaethyl porphyrin, tetrakis methoxyphenylporphine, tetraphenylporphine tetracarboxylic acid, tetrakishydroxyphenyl porphine, tetrakis sulfonatophenyl porphine,etioporphyrin, 1, 10-phenanthroline, 1, 10-phenanthroline-5,6-dionedimethyl-1, 10-phenanthroline, dimethyl-1, 10-phenanthroline,dimethoxy-1, 10-phenanthroline, dimethoxy-1, 10-phenanthroline, amino-1,10-phenanthroline, methyl-1, 10-phenanthroline, dihydroxy-1,10-phenanthroline, tetramethyl-1, 10-phenanthroline, chloro-1,10-phenanthroline, dichloro-1, 10-phenanthroline, nitro-1,10-phenanthroline, bromo-1, 10-phenanthroline, tetrabromo- 1,10-phenanthroline, pyrazino[1, 10]phenanthroline, diphenyl-1,10-phenanthroline, dimethyl diphenyl-1, 10-phenanthroline, ethenylformyl(hydroxy trimethyltetradecyl) trimethyl porphine dipropanoato,diethenyl tetramethyl porphine dipropanoato, bis((aminocarboxyethyl)thio)ethyl tetramethyl porphine dipropanoato, dihydrodihydroxy tetramethyl divinyl porphine dipropionic acid lactonato,ethenyl(hydroxy trimethyl tetradecatrienyl) tetramethyl porphinedipropanoato, carboxyethenyl carboxyethyl dihydro bis(hydroxymethyl)tetramethyl porphine dicarboxylato,(dimethylbenzimidazolyl)cyanocobamide, curtis macrocycle, Jäagermacrocycle and DOTA macrocycle, is coordinated to a metal.
 6. Thenon-noble metal-based catalyst according to claim 5, wherein the metalcomprises at least one transition metal selected from iron (Fe), cobalt(Co), manganese (Mn), nickel (Ni), and chromium (Cr).
 7. The non-noblemetal-based catalyst according to claim 1, wherein the non-noblemetal-based catalyst precursor comprises a transition metal having aweight of about 1 to 50 wt % based on a total weight of the porouscarbon.
 8. The non-noble metal-based catalyst according to claim 1,wherein the porous carbon has an anchoring site introduced into asurface of a pore of the porous carbon to enhance interactions betweenthe porous carbon and the non-noble metal-based catalyst precursor.